Who needs to complete a Self Assessment return?
You need to file a Self Assessment tax return for the 2024–25 tax year (ending 5 April 2025) if any of the following applied to you:
- You were self-employed and your profits exceeded £1,000
- You were a company director (unless your only income was a salary taxed under PAYE)
- Your total taxable income was over £100,000
- You received income from renting out property
- You had foreign income
- You received untaxed income of more than £2,500 (e.g., tips, commission)
- You need to claim certain reliefs (e.g., higher-rate pension tax relief)
- You received Child Benefit and either you or your partner earned more than £60,000
- You were a partner in a business partnership
If you're employed and all your income is taxed through PAYE, you generally don't need to file — unless one of the above applies.
Key deadlines
Ready to run the numbers? Use our free calculator.
Estimate your Self Assessment bill →| Deadline | What it's for |
|---|---|
| 5 October 2025 | Register for Self Assessment if you're doing it for the first time for 2024–25 |
| 31 October 2025 | File your paper return for 2024–25 |
| 31 January 2026 | File your online return for 2024–25 AND pay the tax you owe |
| 31 July 2026 | Second payment on account for 2025–26 (if applicable) |
What you'll need to gather
Before starting your return, pull together:
- P60 or P45 — shows your total employment income and tax paid
- P11D — shows any benefits in kind from your employer
- Self-employment records — total income and allowable expenses (keep these for at least 5 years)
- Bank interest statements — from savings accounts
- Dividend vouchers — or your broker's tax certificate
- Rental income and expenses — receipts, mortgage interest statements
- Pension contributions — contributions not made through PAYE (to claim higher-rate relief)
- Gift Aid donations — to claim tax relief
Allowable expenses for the self-employed
You can deduct "wholly and exclusively" business expenses from your profits. Common allowable expenses include: office costs, travel and mileage (business trips, not commuting), advertising, professional fees (accountants, solicitors), training directly related to your trade, and a proportion of home costs if you work from home.
You can use simplified expenses (flat rates for vehicles and home use) or claim actual costs — whichever is more beneficial.
Payments on account
If your Self Assessment tax bill is more than £1,000, HMRC requires you to make advance payments for the following year — called "payments on account". Each payment is half your previous year's bill, due on 31 January and 31 July. This catches many first-time filers off guard: on 31 January you pay last year's tax plus the first payment on account for the current year.
If you expect your income to be lower in the current year, you can apply to reduce your payments on account.
Penalties for late filing or payment
Missing the 31 January deadline incurs an automatic £100 penalty, even if you owe no tax. If the return is more than 3 months late, daily £10 penalties apply (up to £900). Interest is charged on unpaid tax from the due date. Penalties increase significantly for returns more than 6 or 12 months late.
If you have a reasonable excuse (serious illness, bereavement), you can appeal against penalties through HMRC.